This invention relates to pulse time addition circuitry and more particularly to an improved pulse time addition circuit for use in an electronic fuel injection system for insuring that the desired total amount of fuel is added to the engine regardless of the sequence of generation of control pulses.
Many types of electronic fuel injections systems are known in the prior art, such as those shown in U.S. Pat. Nos. 3,548,792; 3,643,635; 3,689,755; 3,750,632; and 3,986,006. Prior art electronic fuel injection systems employ fuel injectors for feeding fuel to an engine. The fuel injectors are turned on and off by electrical pulses whose time period or pulse duration is controlled in accordance with information received from various engine sensors.
Many systems employ a primary pulse which is triggered for each revolution of the engine and this pulse is used to turn on a group of fuel injectors for a controlled time period. Auxiliary pulses for acceleration enrichment are used to turn on the same injectors for time periods that are also controlled. The acceleration enrichment pulses are initiated by a device on the throttle body and are not synchronous with the primary pulses.
In conventional circuits, an acceleration enrichment pulse that occurs during the time period of a primary pulse will not add anything to the total fuel received by the engine and therefore, the total amount of fuel supplied to the engine is less than the combination of the time periods of the primary pulses and auxiliary acceleration enrichment pulses would dictate.
The prior art also teaches a method of generating the primary fuel control pulse in an electronic fuel injection system. A voltage V(map) which varies with the intake manifold absolute pressure (m.a.p.) is connected to the non-inverting terminal of a voltage comparator. A capacitor, which is charged by a charging current, is connected to the inverting input terminal of the voltage comparator. The capacitor is quickly discharged each time a trigger is received from the engine revolution sensor. The primary fuel control pulse T.sub.p is initiated at the time of an engine revolution trigger and is terminated when the voltage on the capacitor reaches the value of V(map).
A non-synchronous acceleration enrichment pulse T.sub.AE is added by means of a logical "OR" gate to provide a logical sum, one input of the gate being connected to the output of the comparator and the other input being connected to the source T.sub.AE pulses. The logical OR gate therefore provides an accurate additive output only so long as no portion of the T.sub.AE pulse occurs during the time period of the primary pulse T.sub.p.
The present invention provides a relatively simple, inexpensive, highly reliable circuit for providing the required additive pulse output regardless of whether the acceleration enrichment pulse T.sub.AE occurs within or without the time period of the primary pulse T.sub.p.